The risk for heart disease increases dramatically with advancing age. Before the age of menopause, the risk for heart disease in women is reduced compared to that of men; however, after menopause the risk in women increases to a level greater than that of men. Although an age related decrease in coronary blood flow capacity may contribute to the increased risk of heart disease in both males and females, little is known of the interactive effects of age and estrogen on vasoreactivity of the coronary resistance vasculature, the major site for control of coronary blood flow. Recent work indicates that age impairs endothelium-dependent, nitric oxide (NO)-mediated vasodilation of coronary resistance arterioles from both male and female rats; however, preliminary data suggest that the mechanistic changes that result in impaired NO-mediated dilation differ between genders. Therefore, the overall aim of this proposal is to determine the mechanisms by which age and estrogen status alter endothelium dependent, NO-mediated vasodilation in coronary arterioles. Aim 1 is to determine the effect of age and estrogen status on cellular signaling mechanisms that regulate NO-mediated dilation in coronary arterioles. Aim 2 is to determine the effects of age and estrogen status on the contribution of nitric oxide synthase (NOS) isoforms to endothelium-dependent dilation and the activity of (NOS) isoforms in coronary arterioles. Aim 3 is to determine the effects of age and estrogen status on mRNA and protein expression of NOS isoforms in coronary arterioles. These studies will identify mechanisms that contribute to the age-related impairment of NO-mediated vasodilation and determine whether estrogen treatment can improve NO-mediated vasodilation thru restoration of these signaling mechanisms. The information gained from this work will increase our understanding of the effects of age and estrogen in the coronary resistance vasculature and provide insight into the mechanisms that contribute to the age-related loss of endothelial function in both males and females. [unreadable] [unreadable] [unreadable]